解封JSON映射，其中密钥是非内置类型

Question

I'm trying to Unmarshal a JSON map, where the key is a non-builtin type. How do I achieve this?

I wrote some example code for what I think the code should look like. Go playground link

package main

import (
    "encoding/json"
    "errors"
    "fmt"
)

type Tier int

func (t *Tier) UnmarshalJSON(data []byte) error {
    switch string(data) {
    case "TIER1":
        *t = 1
    case "TIER2":
        *t = 2
    default:
        return errors.New("Unrecognized")
    }
    return nil
}

func main() {
    jsonData := []byte(`{
        "TIER1": "hello", 
        "TIER2": "world"
    }`)

    unmarshaledData := map[Tier]string{}
    if err := json.Unmarshal(jsonData, &unmarshaledData); err != nil {
        fmt.Print("Error: ", err)
    }
    fmt.Print("Unmarshaled data: ", unmarshaledData)
}

However, I keep on getting this error:

Error: json: cannot unmarshal number TIER1 into Go value of type main.TierUnmarshaled data: map[]

Am I doing anything wrong in my code?

Answer 1

You need to implement UnmarshalText instead of UnmarshalJSON. From the documentation:

Map values encode as JSON objects. The map's key type must either be a string, an integer type, or implement encoding.TextMarshaler.

func (t *Tier) UnmarshalText(data []byte) error {
    switch string(data) {
    case "TIER1":
        *t = 1
    case "TIER2":
        *t = 2
    default:
        return errors.New("Unrecognized")
    }
    return nil
}

https://play.golang.org/p/6omS7ImuvRl